基于网络编码的无线协作数据交换延迟最优化机制的研究

In recent years, there has been a growing demand in large file downloads and video applications for wireless clients. However, it is not efficient for all the clients to download all the files from the servers directly, as the heavy load might be suffered at the servers. Inspired by peer-to-peer content delivery systems, one solution to address these issues is to allow wireless clients to cooperatively exchange data among themselves, named cooperative data exchange. In cooperative data exchange, each client initially holds a subset of packets, and wants all the packets that others have. Recent literatures on cooperative data exchange got good results on optimizing the total number of transmissions, the total tranmsission cost and etc, during data exchange process. However, none of work studies the minimum tranmsission delay, which is especially important for video applications. In this project, we aim to propose a delay efficient cooperative data exchange scheme, which exploits the benefits of both network coding and wireless tranmsission rate selection. The detail researches include: 1) for time critical applications, the cooperative data exchange scheme to be proposed is to maximize the total number of packets that are received/decoded at the clients without missing their deadlines; 2) under the circumstance of multiple possible transmission rates at the clients, we try to minimize the total transmission delay during the data exchange process, by analyzing the impact of the transmission rate selection on the transmission delay; 3) we further investigate the impact of transmission rate selection on time critical applications, and design a network coded based transmission scheme, so as to maximize the total number of the packets that are timely received at the clients.

新型网络应用和服务的不断涌现使网络用户数量和用户对带宽的需求量持续增长，因此，设计高效的传输策略以缓解网络的高通信量成为当前研究的重要议题。研究显示，利用小范围内的无线协作数据交换不仅可以满足用户的需求，而且可以缓解服务器端的通信瓶颈。本项目拟开展基于网络编码的协作数据交换过程，通过利用网络编码在无线网络吞吐量上的优势和考察无线发送速率对传输延迟等的影响，设计低延迟、高效的协作数据交换机制。具体研究内容包括：1）在单速率无线环境下，研究具有时延约束的协作数据交换过程，设计高效的协作数据交换策略以满足尽可能多的数据包能在时延要求前顺利被接收；2）在多速率无线环境下，分析发送速率选择对数据交换过程中传输延迟的影响，并在此基础上进一步优化传输延迟；3）研究无线发送速率选择对具有时延约束的协作数据交换过程的影响，拟通过速率选择尽可能满足数据包的时延约束，并在此基础上进一步最优化协作数据交换代价。

新型网络应用和服务的不断涌现使网络用户数量和用户对带宽的需求量持续增长。因此，设计高效的数据传输策略以缓解无线网络的高通信量成为当前研究热点之一。本项目利用网络编码技术在无线网络传输上的优势，设计基于网络编码的高效数据传输策略，并取得以下研究成果：1）传输代价最优化策略的研究：针对协作式数据交换过程中传输代价最优化问题，本项目理论分析了当交换的数据信息为链路状态信息时，各无线节点所需发送的数据包个数的充分必要条件，并给出了两种确定性数据发送策略以及相应的数据包编、解码方案；2）传输延迟最优化策略的研究：针对具有转发节点的数据交换过程，本项目设计转发节点处数据包的上载、下载传输过程，以及相应的网络编码方案，从而降低总传输延迟；3）时延感知的协作式数据交换策略的研究：项目提出一种时延感知的协作数据交换策略，设计相应的发送节点及其速率选择机制、数据包编码方案，从而满足数据包的实时性要求。.在本项目的资助下，共发表了18篇SCI/EI学术论文，其中包括在国际期刊IEEE Transactions on Mobile Computing (TMC), IEEE/ACM Transactions on Networking (TON), IEEE Transactions on Vehicular Technology (TVT), IEEE Transactions on Intelligent Transportation Systems(TITS)等上发表SCI检索论文12篇；在国际会议IEEE International Conference on Computer Communications (INFOCOM)，IEEE Global Communications Conference (GLOBECOM), IEEE International Conference on Communications (ICC)等上发表EI检索论文5篇；申请发明专利1项。